Duchenne muscular dystrophy is a common inherited disease, affecting approximately 1 in 3000 live male births. Currently, there is no effective therapy for this disease, however, new therapies are being proposed that offer hope to patients and their families. These therapies must be evaluated for their efficacy in the most stringent manner possible, and in the case of DMD, that requires an appropriate animal model. The long term GOAL of this project is to characterize the molecular defects present in 3 new canine models of dystrophin deficiency. It is hypothesized that these models accurately reflect the depth and breadth of mutations and their effects that is seen in the human population. Current murine models require that multiple genes be knocked out to show the same disease that the loss of dystrophin causes in boys. The canine model system is the only model which appropriately reflects the relentlessly progressive and ultimately fatal disease of boys. However, the complexity of the dystrophin gene and thus the variety of mutations possible, require the availability of multiple models in which to test therapies. The best source of these models continues to be spontaneously occurring canine disease. This severely handicaps the utility of these models in evaluating new therapies. This project will not only elucidate the mutation in these three new canine models, but it will also create a set of tools that will allow investigators worldwide to rapidly evaluate further spontaneous cases of canine muscular dystrophy for their usefulness, both in exploring new therapies and in gaining new insight into the mechanism behind Duchenne muscular dystrophy. Specifically, we propose to use panels of monoclonal antibodies with known specificity to dystrophin, simultaneously with PCR amplification of the coding sequence to rapidly scan for mutations. Suspicious areas will be sequenced to determine if the mutation is contained within. Once the mutations are identified, their effect on transcription, translation and the presence of dystrophin will be evaluated and compared to similar human mutations to determine if there is a pathophysiological correlation between species and their mutations. Successful completion of this project will result in the addition of three models of human dystrophin deficiency to the tools available to investigators seeking novel treatments. The correlation of these mutations with the clinical course of the disease will allow therapies to be evaluated under a variety of clinical circumstances. These mutations will provide new and different genetic backgrounds upon which various therapies, and in particular genetic therapies, may be examined in a large, outbred animal species.